CA2084816A1 - Integrated optical mirror and its production process - Google Patents
Integrated optical mirror and its production processInfo
- Publication number
- CA2084816A1 CA2084816A1 CA002084816A CA2084816A CA2084816A1 CA 2084816 A1 CA2084816 A1 CA 2084816A1 CA 002084816 A CA002084816 A CA 002084816A CA 2084816 A CA2084816 A CA 2084816A CA 2084816 A1 CA2084816 A1 CA 2084816A1
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- CA
- Canada
- Prior art keywords
- wall
- layer
- cavity
- guide
- mirror
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/14—External cavity lasers
- H01S5/141—External cavity lasers using a wavelength selective device, e.g. a grating or etalon
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Optical Integrated Circuits (AREA)
- Optical Couplings Of Light Guides (AREA)
- Optical Elements Other Than Lenses (AREA)
Abstract
DESCRIPTIVE ABSTRACT
Integrated optical mirror and its production process.
The optical mirror incorporates a lightguide (20) produced on a surface (23) of a substrate (22) and used for the propagation of B light beam (36) in a direction parallel to said surface, a cavity (30) made in the lightguide (20) and having in the propagation direction a first (32) and u second (34) walls oriented perpendicular to said direction and having in section approximately the shape of a circular arc, the distance (L) separating the two walls being equal to the radius of curvature (R) of the second wall at the optical axis (37) of the mirror and a reflecting material layer (38) deposited solely on the second wall in order to reflect the light beam towards the first wall, the second wall forming a concave reflect-ing surface.
(Fig. 2) B 11055.3 LC
Integrated optical mirror and its production process.
The optical mirror incorporates a lightguide (20) produced on a surface (23) of a substrate (22) and used for the propagation of B light beam (36) in a direction parallel to said surface, a cavity (30) made in the lightguide (20) and having in the propagation direction a first (32) and u second (34) walls oriented perpendicular to said direction and having in section approximately the shape of a circular arc, the distance (L) separating the two walls being equal to the radius of curvature (R) of the second wall at the optical axis (37) of the mirror and a reflecting material layer (38) deposited solely on the second wall in order to reflect the light beam towards the first wall, the second wall forming a concave reflect-ing surface.
(Fig. 2) B 11055.3 LC
Description
208A~16 INTEGRATED OPTICAL MIRROR AND ITS PRODUCTION PROCE_S
DE~CRIPTION
The present invention relates to 8 mirror for integrated optics, as well to its production procsss. It is used in all fields ~here it is ~ished to reflect a light beam snd in particulsr in the field of real time radar signal processing, e.g. in correlstors, spectrum analyzers or interferometers, in the field of optical communications and in the field of optical fibre sensors and transducers. The latter are in particular used in the space, naval, automobile and aeronautical fields, as ~ell as on production lines for a largs number of objects. ~ore specific-ally, said mirror is intended to equip an e~ternsl cavity for the stabilization of a semiconductor laser diode.
Information processing snd/or remote trans-mitting methods investigated over the last fe~ years utilize transmission by light ~ave in planar light-guides. These lightguides are constituted by a guiding layer intercalated bet~een t~o upper and lo~er confinement layers stacked on a substrate, the guiding layer having 8 real refractive inde~ higher than that of the upper and lo~er layers. In certain cases, the upper layer can be replaced by air.
Integrated optical mirrors constitute one of the basic components of all planar guide structure integrated optical circuits.
At present, the easiest way to produce a mirror in integrated optics is sho~n in longitudinal section in the attached Fig. 1. It is possible to see therein a substrate 2 supporting a lightguide 3 con-stituted by the lower confinement layer 4 or buffer layer, then the guide layer 6 und finally the upper confinement layer 8.
11055.3 LC
208~816 The construction of the ~irror consists of entirely etching the layers 4, 6 snd 8 of the guide up to the substrate and covering the etched flank 10 by a metallizing costing 12, in order to reflect the incident beam 14 transmitted by the layer 6 to the guide layer 6 again. The reflected beao carries the reference 15. The metallizin~ coating 12 can be replaced by a stac~ of dielectric coatings servir~ a8 a ~irror.
This type oP oirror is in particular used for guide structures formed on silicon substrates, e.g. of type Si/SiO2/Si3N4/SiO2, called OISl, or of tgpe Si/SiO2/doped SiO2/SiO2 , called OIS2 . The doping of the guide layer is such that its refractive 11 indes is higher than that of the upper and lo~er con-fine~ent layers.
The difficulties in producinK such a mirror ~re essentially linked ~ith the etching of the actual guide structure for the t~o follo~ing reasons:
- th~ etching thichness of the guide structure can be significant, e.g. 25 to 30 ~, for sn OIS2 struc-ture used for optical communication;
- the quality of the etching fro~ the surface state standpoint and in particular the profile of the flanh 10 plays an essential part ~ith regards to the vslue of the reflection coefficient of the ~irror.
Everything ~ould be perfect, ir the etchin~
of the guide structure ~as perfectly perpendicular to the plane of the guide layers. Unfortunately this situation does not esist and the true profiles of the oirrors differ to ~ varying estent coopared ~ith the ideal profile leading to a rapid drop in the re-flection coefficient. The latter increases ~s the incidence of the light bean 14 carried b~ the guide layer approschQs the perpendicular to the irror (or etched flank 10).
B 11055.3 LC
208~816 In OIS2-type structures, the light loss on reflection in the optimum cases reaches close to 3 dB ~i.e. 50X) compared with the ideal value.
An obvious solution would be to use technical processes leading to etching of the guide structure close to the ideal profile sought for mirrors.
Although advances are to be hoped for in this field, this ~ill lead to long, tedious and therefore e~pen-sive research, ~hich will hardly ever lead to the absolutely ideal solution.
The present invention is directed at an integrated optical mirror and its production process mahing it possible to obviate these disadvantages. In particular, it mahes it possible to produce mirrors having reflection coefficients equal to the theoreti-cal coefficient, ~hilst still using conventional mirror production methods.
The principle of the invention is to carry out the reflection of the instant beam on the second and not the first etched flank of the guide structure encountered by the incident beam, ~hilst using con-ventionally obtained etching profiles. In section, these etching flanhs are shaped like a circular arc, ~hose centre is roughly located on the opticsl a~is of the mirror.
More specifically, the invention relates to an integrated optical mirror having a lightguide produced on a surface of a substrate and used for the propagation of a light beam in a direction parallel to said surface, a cavity made in the lightguide having in the propagation direction a first and a second walls oriented perpendicular to said direction and in section appro~imately having the shape of a circular arc, the distance separating the t~o ~alls being equal to the radius of curvature of the second wall at the optical a~is of the mirror, and a reflecting material 11055.3 LC
~ 4 ~ 2084816 layer deposited solely on the second ~all in order to reflect said light beam to the first ~all, the second wall forming a concaYe reflecting surface.
Unlike in the case of the prior srt inte-grated mirrors, the first ~all encountered by theincident beam is not covered ~ith a reflecting layer and consequently does not reflect the incident beam.
In order to improve the efficienc~ of the mirror and in particular reduce the divergence angle of the light guided in the cavity, the latter can ad-vantageously be filled ~ith a dielectric material, which also provides u mechanical protection for the mirror.
The integrated mirror according to the invention can be a parabolic, elliptical or "plane"
mirror. In the t~o former cases, the cross-section in the plane of the guide of the second ~all is respect-ively parabolic or elliptical and the first ~all is such that the distance sepsrating it from the second wall is constant.
The mirror according to the invention can also be an optionally parabolic or elliptical Fresnel-type mirror. In this case, the second ~all is consti-tuted by several adjacent facets ensuring both the reflection of the light beam and its dispersion and the first ~all follo~s the profile of the second ~all in such a ~ay that the distance separating it from the second ~all is constant or quasi-constant.
In practice, the distance separating the t~o 30 ~alls is 10 to 100 ~m. The precision on this distance is sppro~imately lOX, ~hich causes little problem and enables the mirrors according to the invention to function correctly for all radii invol~ed, no matter ~hether their incidence on the second ~all is per-pendicular or not to the latter, unlike in the case of the prior art.
B 11055.3 LC
208~816 In hnown manner, the lightguide comprises a lo~er confinement layer, a guide layer and an upper confinement layer, the guide layer being interposed between the confinement layers havîng a refractive inde~ higher than that of the confinement layers.
According to the invention, the cavity extends from the upper layer to the lower layer of the guide structure, so that the light rays can freely diverge in the cavity and reach the second wall ~ithout any obstacle.
The mirror according to the in~ention can be produced on a large number of substrates and in par-ticular on glass, lithium niobate, silicon, III - V
materials and e.g. on GaAs or InP, or on II - VI
materials, e.g. CdTe.
In particular, the mirror according to the invention is applicable to the follo~ing structures:
- glass/glass doped by ion e~change/SiO2 si/si2/si3N4/si2 20 ~ Si/SiO2/A12O3/SiO2 - Si/SiO2/SiO~Ny/SiO2 with o~x<2 and O<y<4/3, - Si/SiO2/doped SiO2/SiO2.
The dopants of the silica guide layer are such that the latter hss 8 refractive inde~ higher than that of the adjacent layers.
In addition, the silica of the confinement layers can be used in pure or doped form. When the latter is doped by a dopant reducing its refractive inde~, the guide layer can option~lly be produced from undoped silica.
The doping of the silica by a material in-creasing its refractive inde~ can be carried out by phosphorus, germanium, titanium or nitrogen and the doping of the silica by a dopant reducing its refract-ive inde~ csn be carried out by boron or fluorine.
B 11055,3 LC
Obviously, the guide layer must still ha~e a refract-ive inde~ higher than that of the confinement l~yers.
It is also possible to replace the silicon substrate by a silic8 substrate.
In a structure of the OISl or OIS2 type, the dielectric material used optionnlly for the filling of the cavity has a refractive inde~ close to that of the pure or doped silica or, in the case of a guide having a large inde~ difference, close to the effective inde~
of the guided mode.
The invention also relates to a process for the production of an integrated optical mirror of the type described hereinbefore. This process consists of forming the lightguide on the face of the substrate, producing a photosensitive resin mas~ on the light-guide, having an opening facing the location of the cavity to be produced, eliminating the unmssked area of the lightguide, eliminating the resin mas~ and depositing on the second wall a reflecting material layer using a precursor ion beam of said material inclined with respect to the surface of the guide.
For OISl and OIS2 structures, the circular arc walls of the trench are obtained naturally by using reactive ionic etching using as the etching gas a fluorine-containing gas such as in particulHr CF4, CHF3, C2F4 or SF6, preference being given to C~F3.
The invention also relates to a semicon-ductor laser diode stabilized by an e~ternal cavity formed in a lightguide for the propagation of a light beam emitted by the diode in a given direction, said cavity having in the direction of the propagation a first and a second walls oriented perpendicular to said direction and, in section, appro~imately having the shape of a circular arc, the distance separating the t~o walls being equal to the radius of curvature B l1055.3 LC
~ 7 ~ 208~816 of the second wall at the optical axis of the e~ternal cavity, and a layer of a reflecting material deposited solely on the second wall in order to reflect said light beam to the first wall, the second wall forming a concave reflecting surface, the first ~all of the cavity constituting an input face of the diode.
The invention is described in greater detail hereinafter relstive to non-limitative embodiments and ~ith reference to the attached dra~ings, ~herein sho~:
10 Fig. 1 Already described, diagrammatically and in longitudinal section a prior art integrated optical oirror.
Fig. 2 Diagrammatically and in longitudinal section a plane" integrated optical mirror according to the invention.
Fig. 3 Diagrammatically and in plan vie~ an integrated elliptical or parsbolic mirror according to the invention.
Fig. 4 Diagrammatically and in plan vie~ a Fresnel-type integrated optical mirror according to the invention.
Figs. 5a and 5b Diagrammatically the different stages of the production of an integrated mirror according to the invention in a first variant.
~ig. 6 Diagrammatically and in longitudinal section, a constructional variant of an integrated mirror according to the invention.0 Figs. 7a and 7b Diagrammatically the different stages of the production of an integrated mirror according to the invention, in a second variant.
Figs. 8 and 9 Diagrammatically, respectively in longitudinal section and in plan vie~, a laser diode stabilized by an B 11055.3 LC
~ 8 - ~2Q8~816 e~ternal cavity snd constituted by a mirror according to the invention.
Fig. 2 diagrammatically shows an integrated "plane~ mirror according to the invention in the form of a sectional vie~ in a plane perpendicular to the light propagation plane in the guide structure.
As for the prior art, the optical mirror according to the invention is formed in a guide structure 20 resting on the upper surface 23 of a sub-strate 22, e.g. of silicon or silica.
The guide structure 20 is constituted bythree superimposed layers, namely a lower confinement layer 24 of pure or doped silica, a guide layer 26 oE
alumina, silicon nitride, silicon o~ynitride or silica (pure or doped) having a high refractive inde~ and an upper confinement laYer 28 of pure or doped silica.
The silica of these la~ers can be doped either by a dopsnt reducing its refrsctive inde~
(boron or fluorine) or by a doPant increasing its refractive inde~ ~germanium, nitrogen, phosphorus, titanium). The doping of the silica must be such that the guide layer 26 has a refractive inde~ higher than that of the layers 24 and 28.
For an OIS1 structure, the layers 24, 26 and 25 28 respectively have thicknesses of 1 to 8 ~m, 10 to 250 nm and 1 to 8 ~m. For an ~IS2 structure, the layers 24, 26 and 28 respectively have thichnesses of 6 to 15 ~m, 1 to 10 ~m and 2 to 12 ~m.
According to the invention, the guide structure 20 has a cavity 30 defined by etching the stack of layers 24, 26, 28. This cavity 30 has sn input ~all 32 (or first ~all) and an output wall 34 (or second ~all) oriented perpendicular to the incident beam 36 carried by the guide layer in a direction parallel to the substrate surface 23, parallel to the plane of the guide. In the plane of B 11055.3 LC
Fig. 2, the walls 32 and 34 have the appro~imate 2 0 8 4 816 shape of a circular arc, whose centres, respectively C
and C', are roughly located on the optical a~is 37 of the mirror.
,5 According to the invention, the distance separating the walls 32, 34 of the cavity 30 and des-ignated L is equal to the radius of curvature R of the ~all 34. In practice, the distance L is appro~imately 10 to 100 ~m. Its accuracy is appro~imately lOX, ~hich does not cause any problem and enables the mirror according to the invention to operate for all light rays involved.
The precise shape of the walls is dependent on the cavity etching conditions and can therefore, to a certain e~tent, be adapted to take account of special features of the different vave guides (partic-ularly the numerical aperture).
The second wall 34 defines a concave mirror for the incident beam 36 and is used for reflecting the incident light to the wall 32. The reflected beam carries the reference 39.
According to the invention, a layer 38 of a reflecting material, e.g. metal is deposited solely on the cavity wall 34. This layer 38 is in particular of aluminium, gold, silver, etc. and has a thickness of typically 50 to 1000 nm.
~ he input ~all 32 of the cavity 30 also has, in section, the shape of a circular arc.
In the embodiment shown in Fig. 2, the wall 32 generally has a concavity reverse of that of the wall 38. It ensures a divergence of the incident beam 36 by an angle A with respect to the optical a~is 37 of the mirror.
Fig. 3 diagrammatically sho~s a parabolic or elliptical mirror according to the invention. Fig. 3 is a plan view of said mirror and is therefore in the B 11055.3 LC
208~816 plane of the guide. In this type of mirror, for a light source point S in the guide laYer 26, the focussing point F is displaced in the plane of the guide parallel to the substrate surface 23. The source point S can be supplied either by an integrated diopter (integrated lens of the Fresnel type or the like) or by the end of a light microguide. The focussing point F can also correspond to the end of a microguide. In general, S and F are located on the first wall 32A.
As hereinbefore, only the second wall 34a of the cavity 30a encountered by the incident beam 36 is covered with a reflecting layer 38. According to the invention, only said reflecting face 34a strictly needs to be parabolic or elliptical depending on whether the said mirror is a parabolic or elliptical mirror. The input wall 32a of the cavity 30a, which is only used for diffracting the incident light 36, follows the profile of the ~all 34a in such a way that the distance L sepurating the surface 32a fro~ the surface 34a remains constant from the bottom of the c~vity to its surface. Thus, the wall 32a has a con-cavity identical to that of the wall 34a and therefore has an elliptical or parabolic shape.
Fig. 4 diagrammatically sho~s in plan vie~ a dispersive, Fresnel-type integrsted mirror according to the invention. This mirror has a cavity 30b, ~hereof the second ~all 34b has the general shape of a circular arc in a plane perpendicular to the propa-gation plane ~i.e. in a plane perpendicular to that of Fig. 4~. Moreover, said wall 34b is constituted by multiple facets 40, which ensure both the reflection of the incident light 36 and its dispersion as a function of the ~avelength.
Thus, said mirror for a light source point S' ~ith multiple wavelengths in the guide layer and in particular wavelengths A1 and A2, has focussing points of the wall 34b of the cavity 30b and therefore the mirror displaced in the plane of the guide ~y F~1 and ~2. `As hereinbefore, the points S', FA1 and FA2 can correspond to ends of light microguides produced in a prior operatio~, the orientation of the microguid~ in which the light is refocussed is chosen so as to favour the light coupling ~generally in the direction of the median ray).
The mirror of Fig. 4 is in particular an elliptical mirror.
As for the mirror shown in Fig. 3, the second wall 34b of the cavity 30b is covered with a reflecting layer 38. Moreover, the first wall 32b encountered by the incident beam 36 follows the pro-file of the ~all 34b at a distance L equal to the mean radius of curvature of the wall 34b.
Bearing in mind the small displacements of the facets 40, typically 1 ~m, it is not necessary to reproduce these facets on the ~all 32b. Therefore the latter can follow the envelope 42 of the ~all 34b.
In addition, as in the embodiment of Fig. 3, the two ~alls 32b and 34b have a concave shape.
The follo~ing description relates to the production of an optical mirror sccording to the invention. The description relates to a "plane"
optical mirror like that shown in Fig. 2. However, it is obvious that this process also applies to the pro-duction of other types of mirror.
With reference to Fig. 5a, the first stage of the process consists of forming the lightguide 20 on the surface 23 of the substrate 22 by successively depositing the layers 24, 26 and 28 by thermal o~ida-tion of the substrate for the layer 24 and by option-ally plasma-assisted chemical vapour deposition for B 11055.3 LC
- 12 - 208~16 layers 26 and 28. The layer deposition methods are in accordance ~ith the prior art.
Using conventional photolithography pro-cesses, this is followed by the production of a resin mask 44 having an opening 46 at the location where it is wished to produce the mirror cavity 30. This mask 44 is e.g. produced according to the known three-layer procedure (successive depositions of a lo~er resin layer, a dielectric layer and an upper resin layer, 10~) producing a mask in the upper resin layer, etching the dielectric layer, elimination of the upper resin layer and then using said dielectric mask for etching the lower resin layer and finally eliminating the di-electric mask).
This is follo~ed by a high po~er reactive ionic etching (250 to 400W) of the three layers 28, 26 and 24 of the guide using a fluorine-containing agent 47 and in particular CHF3 at high pressure (>9OmT, i.e. >12Pa in the machine used~. This gi~es a cavity 30 facing the opening 46 of the resin mask 44, whose walls 32 and 34 have, in section, the shape of a circular arc of radius R and whose respective centres C and C' are located on the optical a~is 37. The cavity is barrel-shaped ~ith a ~idth masimum on the optical a~is 37.
The reactive ionic etchi.ng of the silica based on fluorine-containing compounds makes it possible to produce various etched shapes, ~hich are a function of the pressure of the gases used (CHF3~02 or others3, the power used, the o~ygen level and the resistsnce of the mask to the etching agent.
In general terms, under high power and high pressure, the number of collision~ bet~een the etching agent and the material to be etched increases and tends to decrease the anisotropy of the etching. This would consequently lead to a non-vertical etching with B 11055.3 LC
208g816 a maximum opening on the bottom, but in practice the mas~, if it is able to resist the etching well (good selectivity), will oppose the obtainin~ of this shape, ~hich is the case with a three-layer mask (thick resin/SiO2/thin resin).
Unlike in the invention, ~ith silica thick-nesses smaller than those used here and in particular ~ith OISl structure, it is possible to work at a lo~er po~er snd lo~er pressure and thus obtain more vertical profiles.
Follo~ing the elimination of the resin mask 44, e.g. ~ith the aid of an adapted solvent or an o~ygen plasma, in the manner sho~n in Fig. 5b, the metal layer 38 is deposited on the ~all 34 of the cavity 30. This deposit is brought about by supplying an ion beam 48, e.g. through a metal mask 49, inclined by an angle B relative to the surface of the guide 20.
Typically B is 20 to 80 for L of 10 to 100 ~m. This ion beam 48 can result from a vacuum evaporation or a cathodic sputtering.
As a result of the inclination, the wall 32 is not generally touched or affected by the metalliza-tion and the e~cess metal can then be removed by etching. In this case, the metallization of the ~all can tahe Place without a mash 49.
It is also possible to use the lift off pro-cedure (deposition of a resin mask, metallization, elimin~tion of the resin and the metal covering it) for forming the deposit 38.
It is also possible to replace the metal deposit by a dielectric multilayer deposit, using the same principle.
Fig. 6 sho~s diagrammatically and in section a constructional variant of the mirror according to the invention. In this variant, the mirror differs B 11055.3 LC
from those described hereinbefore by the filling of the cavity 30 with a dielectric material 50 having a refractive index preferably close to that of the guide layers 2~, 26 and 28 and therefore, in the present case, pure silicu or doped silica, or in the case of significant refractive index differences, close to the effective inde~ of the guided mode (case of OISl guides). In particular, said dielectric 50 can be 5ilica gel or an optical adhesive or glue.
This dielectric 50 provides a mechanical protection for the mirror. It also improves the efficiency of the mirror by reducing the divergence angle A' of the light guided in the cavity 30. It also reduces light losses by Fresnel-type reflection on the first wall 32 of the cavity.
The cavity 30 can be filled either by chemicsl vapour deposition, or with a syringe follo~-ing the previously etched filling circuits, or by using a whirler.
In the case of guide structures constituted by very different materials, such as Si/SiO2/Si3N4/
SiOz or Si/SiO2/A1203/SiO2 structures, the etching of the core material (Si3N4 or A1203) can be different from that of the surrounding materials (SiO2).
In this case, the mirror is advantageously produced in the manner shown in Figs. 7a and 7b:
- 1) - deposition of the lower 24 and guide 26 layers of the guide structure;
DE~CRIPTION
The present invention relates to 8 mirror for integrated optics, as well to its production procsss. It is used in all fields ~here it is ~ished to reflect a light beam snd in particulsr in the field of real time radar signal processing, e.g. in correlstors, spectrum analyzers or interferometers, in the field of optical communications and in the field of optical fibre sensors and transducers. The latter are in particular used in the space, naval, automobile and aeronautical fields, as ~ell as on production lines for a largs number of objects. ~ore specific-ally, said mirror is intended to equip an e~ternsl cavity for the stabilization of a semiconductor laser diode.
Information processing snd/or remote trans-mitting methods investigated over the last fe~ years utilize transmission by light ~ave in planar light-guides. These lightguides are constituted by a guiding layer intercalated bet~een t~o upper and lo~er confinement layers stacked on a substrate, the guiding layer having 8 real refractive inde~ higher than that of the upper and lo~er layers. In certain cases, the upper layer can be replaced by air.
Integrated optical mirrors constitute one of the basic components of all planar guide structure integrated optical circuits.
At present, the easiest way to produce a mirror in integrated optics is sho~n in longitudinal section in the attached Fig. 1. It is possible to see therein a substrate 2 supporting a lightguide 3 con-stituted by the lower confinement layer 4 or buffer layer, then the guide layer 6 und finally the upper confinement layer 8.
11055.3 LC
208~816 The construction of the ~irror consists of entirely etching the layers 4, 6 snd 8 of the guide up to the substrate and covering the etched flank 10 by a metallizing costing 12, in order to reflect the incident beam 14 transmitted by the layer 6 to the guide layer 6 again. The reflected beao carries the reference 15. The metallizin~ coating 12 can be replaced by a stac~ of dielectric coatings servir~ a8 a ~irror.
This type oP oirror is in particular used for guide structures formed on silicon substrates, e.g. of type Si/SiO2/Si3N4/SiO2, called OISl, or of tgpe Si/SiO2/doped SiO2/SiO2 , called OIS2 . The doping of the guide layer is such that its refractive 11 indes is higher than that of the upper and lo~er con-fine~ent layers.
The difficulties in producinK such a mirror ~re essentially linked ~ith the etching of the actual guide structure for the t~o follo~ing reasons:
- th~ etching thichness of the guide structure can be significant, e.g. 25 to 30 ~, for sn OIS2 struc-ture used for optical communication;
- the quality of the etching fro~ the surface state standpoint and in particular the profile of the flanh 10 plays an essential part ~ith regards to the vslue of the reflection coefficient of the ~irror.
Everything ~ould be perfect, ir the etchin~
of the guide structure ~as perfectly perpendicular to the plane of the guide layers. Unfortunately this situation does not esist and the true profiles of the oirrors differ to ~ varying estent coopared ~ith the ideal profile leading to a rapid drop in the re-flection coefficient. The latter increases ~s the incidence of the light bean 14 carried b~ the guide layer approschQs the perpendicular to the irror (or etched flank 10).
B 11055.3 LC
208~816 In OIS2-type structures, the light loss on reflection in the optimum cases reaches close to 3 dB ~i.e. 50X) compared with the ideal value.
An obvious solution would be to use technical processes leading to etching of the guide structure close to the ideal profile sought for mirrors.
Although advances are to be hoped for in this field, this ~ill lead to long, tedious and therefore e~pen-sive research, ~hich will hardly ever lead to the absolutely ideal solution.
The present invention is directed at an integrated optical mirror and its production process mahing it possible to obviate these disadvantages. In particular, it mahes it possible to produce mirrors having reflection coefficients equal to the theoreti-cal coefficient, ~hilst still using conventional mirror production methods.
The principle of the invention is to carry out the reflection of the instant beam on the second and not the first etched flank of the guide structure encountered by the incident beam, ~hilst using con-ventionally obtained etching profiles. In section, these etching flanhs are shaped like a circular arc, ~hose centre is roughly located on the opticsl a~is of the mirror.
More specifically, the invention relates to an integrated optical mirror having a lightguide produced on a surface of a substrate and used for the propagation of a light beam in a direction parallel to said surface, a cavity made in the lightguide having in the propagation direction a first and a second walls oriented perpendicular to said direction and in section appro~imately having the shape of a circular arc, the distance separating the t~o ~alls being equal to the radius of curvature of the second wall at the optical a~is of the mirror, and a reflecting material 11055.3 LC
~ 4 ~ 2084816 layer deposited solely on the second ~all in order to reflect said light beam to the first ~all, the second wall forming a concaYe reflecting surface.
Unlike in the case of the prior srt inte-grated mirrors, the first ~all encountered by theincident beam is not covered ~ith a reflecting layer and consequently does not reflect the incident beam.
In order to improve the efficienc~ of the mirror and in particular reduce the divergence angle of the light guided in the cavity, the latter can ad-vantageously be filled ~ith a dielectric material, which also provides u mechanical protection for the mirror.
The integrated mirror according to the invention can be a parabolic, elliptical or "plane"
mirror. In the t~o former cases, the cross-section in the plane of the guide of the second ~all is respect-ively parabolic or elliptical and the first ~all is such that the distance sepsrating it from the second wall is constant.
The mirror according to the invention can also be an optionally parabolic or elliptical Fresnel-type mirror. In this case, the second ~all is consti-tuted by several adjacent facets ensuring both the reflection of the light beam and its dispersion and the first ~all follo~s the profile of the second ~all in such a ~ay that the distance separating it from the second ~all is constant or quasi-constant.
In practice, the distance separating the t~o 30 ~alls is 10 to 100 ~m. The precision on this distance is sppro~imately lOX, ~hich causes little problem and enables the mirrors according to the invention to function correctly for all radii invol~ed, no matter ~hether their incidence on the second ~all is per-pendicular or not to the latter, unlike in the case of the prior art.
B 11055.3 LC
208~816 In hnown manner, the lightguide comprises a lo~er confinement layer, a guide layer and an upper confinement layer, the guide layer being interposed between the confinement layers havîng a refractive inde~ higher than that of the confinement layers.
According to the invention, the cavity extends from the upper layer to the lower layer of the guide structure, so that the light rays can freely diverge in the cavity and reach the second wall ~ithout any obstacle.
The mirror according to the in~ention can be produced on a large number of substrates and in par-ticular on glass, lithium niobate, silicon, III - V
materials and e.g. on GaAs or InP, or on II - VI
materials, e.g. CdTe.
In particular, the mirror according to the invention is applicable to the follo~ing structures:
- glass/glass doped by ion e~change/SiO2 si/si2/si3N4/si2 20 ~ Si/SiO2/A12O3/SiO2 - Si/SiO2/SiO~Ny/SiO2 with o~x<2 and O<y<4/3, - Si/SiO2/doped SiO2/SiO2.
The dopants of the silica guide layer are such that the latter hss 8 refractive inde~ higher than that of the adjacent layers.
In addition, the silica of the confinement layers can be used in pure or doped form. When the latter is doped by a dopant reducing its refractive inde~, the guide layer can option~lly be produced from undoped silica.
The doping of the silica by a material in-creasing its refractive inde~ can be carried out by phosphorus, germanium, titanium or nitrogen and the doping of the silica by a dopant reducing its refract-ive inde~ csn be carried out by boron or fluorine.
B 11055,3 LC
Obviously, the guide layer must still ha~e a refract-ive inde~ higher than that of the confinement l~yers.
It is also possible to replace the silicon substrate by a silic8 substrate.
In a structure of the OISl or OIS2 type, the dielectric material used optionnlly for the filling of the cavity has a refractive inde~ close to that of the pure or doped silica or, in the case of a guide having a large inde~ difference, close to the effective inde~
of the guided mode.
The invention also relates to a process for the production of an integrated optical mirror of the type described hereinbefore. This process consists of forming the lightguide on the face of the substrate, producing a photosensitive resin mas~ on the light-guide, having an opening facing the location of the cavity to be produced, eliminating the unmssked area of the lightguide, eliminating the resin mas~ and depositing on the second wall a reflecting material layer using a precursor ion beam of said material inclined with respect to the surface of the guide.
For OISl and OIS2 structures, the circular arc walls of the trench are obtained naturally by using reactive ionic etching using as the etching gas a fluorine-containing gas such as in particulHr CF4, CHF3, C2F4 or SF6, preference being given to C~F3.
The invention also relates to a semicon-ductor laser diode stabilized by an e~ternal cavity formed in a lightguide for the propagation of a light beam emitted by the diode in a given direction, said cavity having in the direction of the propagation a first and a second walls oriented perpendicular to said direction and, in section, appro~imately having the shape of a circular arc, the distance separating the t~o walls being equal to the radius of curvature B l1055.3 LC
~ 7 ~ 208~816 of the second wall at the optical axis of the e~ternal cavity, and a layer of a reflecting material deposited solely on the second wall in order to reflect said light beam to the first wall, the second wall forming a concave reflecting surface, the first ~all of the cavity constituting an input face of the diode.
The invention is described in greater detail hereinafter relstive to non-limitative embodiments and ~ith reference to the attached dra~ings, ~herein sho~:
10 Fig. 1 Already described, diagrammatically and in longitudinal section a prior art integrated optical oirror.
Fig. 2 Diagrammatically and in longitudinal section a plane" integrated optical mirror according to the invention.
Fig. 3 Diagrammatically and in plan vie~ an integrated elliptical or parsbolic mirror according to the invention.
Fig. 4 Diagrammatically and in plan vie~ a Fresnel-type integrated optical mirror according to the invention.
Figs. 5a and 5b Diagrammatically the different stages of the production of an integrated mirror according to the invention in a first variant.
~ig. 6 Diagrammatically and in longitudinal section, a constructional variant of an integrated mirror according to the invention.0 Figs. 7a and 7b Diagrammatically the different stages of the production of an integrated mirror according to the invention, in a second variant.
Figs. 8 and 9 Diagrammatically, respectively in longitudinal section and in plan vie~, a laser diode stabilized by an B 11055.3 LC
~ 8 - ~2Q8~816 e~ternal cavity snd constituted by a mirror according to the invention.
Fig. 2 diagrammatically shows an integrated "plane~ mirror according to the invention in the form of a sectional vie~ in a plane perpendicular to the light propagation plane in the guide structure.
As for the prior art, the optical mirror according to the invention is formed in a guide structure 20 resting on the upper surface 23 of a sub-strate 22, e.g. of silicon or silica.
The guide structure 20 is constituted bythree superimposed layers, namely a lower confinement layer 24 of pure or doped silica, a guide layer 26 oE
alumina, silicon nitride, silicon o~ynitride or silica (pure or doped) having a high refractive inde~ and an upper confinement laYer 28 of pure or doped silica.
The silica of these la~ers can be doped either by a dopsnt reducing its refrsctive inde~
(boron or fluorine) or by a doPant increasing its refractive inde~ ~germanium, nitrogen, phosphorus, titanium). The doping of the silica must be such that the guide layer 26 has a refractive inde~ higher than that of the layers 24 and 28.
For an OIS1 structure, the layers 24, 26 and 25 28 respectively have thicknesses of 1 to 8 ~m, 10 to 250 nm and 1 to 8 ~m. For an ~IS2 structure, the layers 24, 26 and 28 respectively have thichnesses of 6 to 15 ~m, 1 to 10 ~m and 2 to 12 ~m.
According to the invention, the guide structure 20 has a cavity 30 defined by etching the stack of layers 24, 26, 28. This cavity 30 has sn input ~all 32 (or first ~all) and an output wall 34 (or second ~all) oriented perpendicular to the incident beam 36 carried by the guide layer in a direction parallel to the substrate surface 23, parallel to the plane of the guide. In the plane of B 11055.3 LC
Fig. 2, the walls 32 and 34 have the appro~imate 2 0 8 4 816 shape of a circular arc, whose centres, respectively C
and C', are roughly located on the optical a~is 37 of the mirror.
,5 According to the invention, the distance separating the walls 32, 34 of the cavity 30 and des-ignated L is equal to the radius of curvature R of the ~all 34. In practice, the distance L is appro~imately 10 to 100 ~m. Its accuracy is appro~imately lOX, ~hich does not cause any problem and enables the mirror according to the invention to operate for all light rays involved.
The precise shape of the walls is dependent on the cavity etching conditions and can therefore, to a certain e~tent, be adapted to take account of special features of the different vave guides (partic-ularly the numerical aperture).
The second wall 34 defines a concave mirror for the incident beam 36 and is used for reflecting the incident light to the wall 32. The reflected beam carries the reference 39.
According to the invention, a layer 38 of a reflecting material, e.g. metal is deposited solely on the cavity wall 34. This layer 38 is in particular of aluminium, gold, silver, etc. and has a thickness of typically 50 to 1000 nm.
~ he input ~all 32 of the cavity 30 also has, in section, the shape of a circular arc.
In the embodiment shown in Fig. 2, the wall 32 generally has a concavity reverse of that of the wall 38. It ensures a divergence of the incident beam 36 by an angle A with respect to the optical a~is 37 of the mirror.
Fig. 3 diagrammatically sho~s a parabolic or elliptical mirror according to the invention. Fig. 3 is a plan view of said mirror and is therefore in the B 11055.3 LC
208~816 plane of the guide. In this type of mirror, for a light source point S in the guide laYer 26, the focussing point F is displaced in the plane of the guide parallel to the substrate surface 23. The source point S can be supplied either by an integrated diopter (integrated lens of the Fresnel type or the like) or by the end of a light microguide. The focussing point F can also correspond to the end of a microguide. In general, S and F are located on the first wall 32A.
As hereinbefore, only the second wall 34a of the cavity 30a encountered by the incident beam 36 is covered with a reflecting layer 38. According to the invention, only said reflecting face 34a strictly needs to be parabolic or elliptical depending on whether the said mirror is a parabolic or elliptical mirror. The input wall 32a of the cavity 30a, which is only used for diffracting the incident light 36, follows the profile of the ~all 34a in such a way that the distance L sepurating the surface 32a fro~ the surface 34a remains constant from the bottom of the c~vity to its surface. Thus, the wall 32a has a con-cavity identical to that of the wall 34a and therefore has an elliptical or parabolic shape.
Fig. 4 diagrammatically sho~s in plan vie~ a dispersive, Fresnel-type integrsted mirror according to the invention. This mirror has a cavity 30b, ~hereof the second ~all 34b has the general shape of a circular arc in a plane perpendicular to the propa-gation plane ~i.e. in a plane perpendicular to that of Fig. 4~. Moreover, said wall 34b is constituted by multiple facets 40, which ensure both the reflection of the incident light 36 and its dispersion as a function of the ~avelength.
Thus, said mirror for a light source point S' ~ith multiple wavelengths in the guide layer and in particular wavelengths A1 and A2, has focussing points of the wall 34b of the cavity 30b and therefore the mirror displaced in the plane of the guide ~y F~1 and ~2. `As hereinbefore, the points S', FA1 and FA2 can correspond to ends of light microguides produced in a prior operatio~, the orientation of the microguid~ in which the light is refocussed is chosen so as to favour the light coupling ~generally in the direction of the median ray).
The mirror of Fig. 4 is in particular an elliptical mirror.
As for the mirror shown in Fig. 3, the second wall 34b of the cavity 30b is covered with a reflecting layer 38. Moreover, the first wall 32b encountered by the incident beam 36 follows the pro-file of the ~all 34b at a distance L equal to the mean radius of curvature of the wall 34b.
Bearing in mind the small displacements of the facets 40, typically 1 ~m, it is not necessary to reproduce these facets on the ~all 32b. Therefore the latter can follow the envelope 42 of the ~all 34b.
In addition, as in the embodiment of Fig. 3, the two ~alls 32b and 34b have a concave shape.
The follo~ing description relates to the production of an optical mirror sccording to the invention. The description relates to a "plane"
optical mirror like that shown in Fig. 2. However, it is obvious that this process also applies to the pro-duction of other types of mirror.
With reference to Fig. 5a, the first stage of the process consists of forming the lightguide 20 on the surface 23 of the substrate 22 by successively depositing the layers 24, 26 and 28 by thermal o~ida-tion of the substrate for the layer 24 and by option-ally plasma-assisted chemical vapour deposition for B 11055.3 LC
- 12 - 208~16 layers 26 and 28. The layer deposition methods are in accordance ~ith the prior art.
Using conventional photolithography pro-cesses, this is followed by the production of a resin mask 44 having an opening 46 at the location where it is wished to produce the mirror cavity 30. This mask 44 is e.g. produced according to the known three-layer procedure (successive depositions of a lo~er resin layer, a dielectric layer and an upper resin layer, 10~) producing a mask in the upper resin layer, etching the dielectric layer, elimination of the upper resin layer and then using said dielectric mask for etching the lower resin layer and finally eliminating the di-electric mask).
This is follo~ed by a high po~er reactive ionic etching (250 to 400W) of the three layers 28, 26 and 24 of the guide using a fluorine-containing agent 47 and in particular CHF3 at high pressure (>9OmT, i.e. >12Pa in the machine used~. This gi~es a cavity 30 facing the opening 46 of the resin mask 44, whose walls 32 and 34 have, in section, the shape of a circular arc of radius R and whose respective centres C and C' are located on the optical a~is 37. The cavity is barrel-shaped ~ith a ~idth masimum on the optical a~is 37.
The reactive ionic etchi.ng of the silica based on fluorine-containing compounds makes it possible to produce various etched shapes, ~hich are a function of the pressure of the gases used (CHF3~02 or others3, the power used, the o~ygen level and the resistsnce of the mask to the etching agent.
In general terms, under high power and high pressure, the number of collision~ bet~een the etching agent and the material to be etched increases and tends to decrease the anisotropy of the etching. This would consequently lead to a non-vertical etching with B 11055.3 LC
208g816 a maximum opening on the bottom, but in practice the mas~, if it is able to resist the etching well (good selectivity), will oppose the obtainin~ of this shape, ~hich is the case with a three-layer mask (thick resin/SiO2/thin resin).
Unlike in the invention, ~ith silica thick-nesses smaller than those used here and in particular ~ith OISl structure, it is possible to work at a lo~er po~er snd lo~er pressure and thus obtain more vertical profiles.
Follo~ing the elimination of the resin mask 44, e.g. ~ith the aid of an adapted solvent or an o~ygen plasma, in the manner sho~n in Fig. 5b, the metal layer 38 is deposited on the ~all 34 of the cavity 30. This deposit is brought about by supplying an ion beam 48, e.g. through a metal mask 49, inclined by an angle B relative to the surface of the guide 20.
Typically B is 20 to 80 for L of 10 to 100 ~m. This ion beam 48 can result from a vacuum evaporation or a cathodic sputtering.
As a result of the inclination, the wall 32 is not generally touched or affected by the metalliza-tion and the e~cess metal can then be removed by etching. In this case, the metallization of the ~all can tahe Place without a mash 49.
It is also possible to use the lift off pro-cedure (deposition of a resin mask, metallization, elimin~tion of the resin and the metal covering it) for forming the deposit 38.
It is also possible to replace the metal deposit by a dielectric multilayer deposit, using the same principle.
Fig. 6 sho~s diagrammatically and in section a constructional variant of the mirror according to the invention. In this variant, the mirror differs B 11055.3 LC
from those described hereinbefore by the filling of the cavity 30 with a dielectric material 50 having a refractive index preferably close to that of the guide layers 2~, 26 and 28 and therefore, in the present case, pure silicu or doped silica, or in the case of significant refractive index differences, close to the effective inde~ of the guided mode (case of OISl guides). In particular, said dielectric 50 can be 5ilica gel or an optical adhesive or glue.
This dielectric 50 provides a mechanical protection for the mirror. It also improves the efficiency of the mirror by reducing the divergence angle A' of the light guided in the cavity 30. It also reduces light losses by Fresnel-type reflection on the first wall 32 of the cavity.
The cavity 30 can be filled either by chemicsl vapour deposition, or with a syringe follo~-ing the previously etched filling circuits, or by using a whirler.
In the case of guide structures constituted by very different materials, such as Si/SiO2/Si3N4/
SiOz or Si/SiO2/A1203/SiO2 structures, the etching of the core material (Si3N4 or A1203) can be different from that of the surrounding materials (SiO2).
In this case, the mirror is advantageously produced in the manner shown in Figs. 7a and 7b:
- 1) - deposition of the lower 24 and guide 26 layers of the guide structure;
- 2) - etching the guide layer in the form of a planar guide or microguide 26a (Fig. 7a) in such a way as to only retain core material upstream of the first wall 32 of the cavity 30 to be produced;
- 3) - deposition of the upper confinement layer 28 on the structure obtained in 2) (Fig. 7a);
B 11055.3 LC
B 11055.3 LC
- 4) - production of the cavity 30 by etching the lo~er and upper confinement layers 24, 28, followed by the deposition of the metal layer 38 (Fig. 7b).
The distance d between the end of the core of the guide 26a and the first wall 32 of the mirror ;s small (a few micrometres).
This process has the advantage of only re-quiring the deep etching of a single material type (in this case silica), whilst avoiding possible etching 10 and therefore profile disengagements of the w811 34 due to etching speed differences of the materials in dry etching.
The previously described mirror and its pro-duction process can advantageously be used for stabi-lizing a semiconductor lsser diode ~ith the aid of ane~ternal cavity.
The advantages of a stability by e~ternal cavity are an operation of the diode on a single longitudinal mode and a frequency stability due to the lack of mode jumping.
Figs. 8 and 9 respectively sho~, in longi-tudinal section and plan vie~, a laser diode stabi-lized by an external cavity equipped ~ith a mirror according to the invention, such as is described relative to Fig. 2.
The diode 52 provided ~ith a planar or confined active zone 54 is hybridized and fi~ed to the substrAte 22 by a metal ~eld 56. This diode is in particular produced from III - V material using hno~n methods. It has an output face 58 and an input face 60, obtained by cleaving, respectirely f~cing a focussing lens 62 for focussing the light 36 emitted by the diode into the optical guide 20, and an e~ternal cavity constituted by the cavity 30 of the mirror according to the invention. The optical a~is B 11055.3 LC
- 16 - 208~816 37 of the mirror and therefore of the external cavity passes through the active zone 54.
The input face 60 of the diode has an anti-reflec~ing coating 64 serving as a semitransparent mirror and constitutes the first mirror wall. The - metal layer 38 formed on the second wall 34 of the mirror according to the invention makes it possible to reflect the light passing out of the semitransparent mirror 64 towards the active zone 54.
The focussing lens 62 is formed at the end of a tongue 66 defined in the optical guide 20 and overhanging a recess 68 made in the substrate 22. The tongue is obtained by carrying out two successive etching processes, the first being performed at the same time as the etching of the cavity 30 and is used for freeing the optical guide, whilst the second is used for freeing the tongue 66 from the substrate and for forming the recess 68. The second etching is a micro~ave etching using reactive gases such as Ar, SF6 and 2 The lens 62 is obtained by melting the end of the tongue 66 by laser illumination at a wavelength absorbed by the silica, such as the emission of a C02 laser.
The distance L sepsrating the diode input face and the metal layer 38 is in this case typically 30 to 300 ~m and is equal to the radius of curvature R
of the mirror. This makes it possible to reinject a ma~imum of light into the diode and to make it 3o oscillate on the e~ternal cavity. In plan view, the reflecting face 3~ of the mirror according to the invention also has a spherical shape with the same radius of curvature R.
B 11055.3 LC
The distance d between the end of the core of the guide 26a and the first wall 32 of the mirror ;s small (a few micrometres).
This process has the advantage of only re-quiring the deep etching of a single material type (in this case silica), whilst avoiding possible etching 10 and therefore profile disengagements of the w811 34 due to etching speed differences of the materials in dry etching.
The previously described mirror and its pro-duction process can advantageously be used for stabi-lizing a semiconductor lsser diode ~ith the aid of ane~ternal cavity.
The advantages of a stability by e~ternal cavity are an operation of the diode on a single longitudinal mode and a frequency stability due to the lack of mode jumping.
Figs. 8 and 9 respectively sho~, in longi-tudinal section and plan vie~, a laser diode stabi-lized by an external cavity equipped ~ith a mirror according to the invention, such as is described relative to Fig. 2.
The diode 52 provided ~ith a planar or confined active zone 54 is hybridized and fi~ed to the substrAte 22 by a metal ~eld 56. This diode is in particular produced from III - V material using hno~n methods. It has an output face 58 and an input face 60, obtained by cleaving, respectirely f~cing a focussing lens 62 for focussing the light 36 emitted by the diode into the optical guide 20, and an e~ternal cavity constituted by the cavity 30 of the mirror according to the invention. The optical a~is B 11055.3 LC
- 16 - 208~816 37 of the mirror and therefore of the external cavity passes through the active zone 54.
The input face 60 of the diode has an anti-reflec~ing coating 64 serving as a semitransparent mirror and constitutes the first mirror wall. The - metal layer 38 formed on the second wall 34 of the mirror according to the invention makes it possible to reflect the light passing out of the semitransparent mirror 64 towards the active zone 54.
The focussing lens 62 is formed at the end of a tongue 66 defined in the optical guide 20 and overhanging a recess 68 made in the substrate 22. The tongue is obtained by carrying out two successive etching processes, the first being performed at the same time as the etching of the cavity 30 and is used for freeing the optical guide, whilst the second is used for freeing the tongue 66 from the substrate and for forming the recess 68. The second etching is a micro~ave etching using reactive gases such as Ar, SF6 and 2 The lens 62 is obtained by melting the end of the tongue 66 by laser illumination at a wavelength absorbed by the silica, such as the emission of a C02 laser.
The distance L sepsrating the diode input face and the metal layer 38 is in this case typically 30 to 300 ~m and is equal to the radius of curvature R
of the mirror. This makes it possible to reinject a ma~imum of light into the diode and to make it 3o oscillate on the e~ternal cavity. In plan view, the reflecting face 3~ of the mirror according to the invention also has a spherical shape with the same radius of curvature R.
B 11055.3 LC
Claims (14)
1. Integrated optical mirror having a lightguide (20) produced on a surface (23) of a substrate (22) and used for the propagation of a light beam (36) in a direction parallel to said surface, a cavity (30, 30a, 30b) made in the lightguide (20) having in the propagation direction a first (32, 32a, 32b) and a second (34, 34a, 34b) walls oriented perpendicular to said direction and in section approximately having the shape of a circular arc, the distance (L) separating the two walls being equal to the radius of curvature (R) of the second wall at the optical axis (37) of the mirror, and a reflecting material (38) layer deposited solely on the second wall in order to reflect said light beam to the first wall, the second wall forming a concave reflecting surface.
2. Integrated mirror according to claim 1, having a parabolic or elliptical shape, characterized in that the cross-section in the plane of the guide of the second wall (34a) is respectively parabolic or elliptical and in that the first wall (32a) is such that the distance separating it from the second wall is constant.
3. Integrated mirror according to claim 1 of the Fresnel type, characterized in that the second wall (34b) is constituted by several adjacent facets (40) ensuring both the reflection of the light beam and its dispersion and in that the first wall (32b) follows the profile (42) of the second wall, in such a way that the distance (L) separating the second wall is constant or quasi-constant.
4. Integrated mirror according to claim 1, characterized in that the distance (L) separating the B 11055.3 LC
two walls is 10 to 100 µm with an accuracy of approxi-mately 10%.
two walls is 10 to 100 µm with an accuracy of approxi-mately 10%.
5. Integrated mirror according to claim 1, characterized in that the cavity (30) is filled with a dielectric material (50) providing a mechanical pro-tection for the mirror.
6. Integrated mirror according to claim 1, characterized in that the lightguide comprises a lower confinement layer (24), a guide layer (26, 26a) and an upper confinement layer (28), the guide layer (26, 26a) being interposed between the confinement layers and having a refractive index higher than that of the lower and upper layers and in that the cavity (30, 30a, 30b) extends from the upper layer to the lower layer.
7. Integrated mirror according to claim 6, characterized in that the substrate (22) is made from silicon or silica, the upper layer (28) and the lower layer (24) are pure or optionally doped silica layers and the guide layer (26, 26a) is made from doped silica, alumina, silicon nitride or silicon oxynitride.
8. Integrated mirror according to claim 7, characterized in that the cavity is filled with a material having a refractive index close to that of the pure or doped silica or close to the effective index of the guided mode.
9. Integrated mirror according to claim 6, characterized in that the guide layer is etched (26a) in such a way that it only remains upstream of the first wall (32).
10. Process for the production of an integrated optical mirror having a lightguide (20) produced on a surface (23) of a substrate (22) and used for the propagation of a light beam (36) in a direction parallel to said surface, a cavity (30, 30a, B 11055.3 LC
30b) made in the lightguide (20) having in the propa-gation direction a first (32, 32a, 32b) and a second (34, 34a, 34b) walls oriented perpendicular to said direction and in section having approximately the shape of a circular arc, the distance (L) separating the two walls being equal to the radius of curvature (R) of the second wall at the optical axis (37) of the mirror, characterized in that it comprises forming the lightguide (20) on the surface (23) of the substrate (22), producing a photosensitive resin mask (44) on the lightguide, having an opening (46) facing the location of the cavity to be produced, eliminating the zone of the lightguide which is not masked, eliminating the resin mask (44) and depositing on the second wall a reflecting material layer (38) using a precursor ion beam (48) of said material, inclined with respect to the surface of the guide.
30b) made in the lightguide (20) having in the propa-gation direction a first (32, 32a, 32b) and a second (34, 34a, 34b) walls oriented perpendicular to said direction and in section having approximately the shape of a circular arc, the distance (L) separating the two walls being equal to the radius of curvature (R) of the second wall at the optical axis (37) of the mirror, characterized in that it comprises forming the lightguide (20) on the surface (23) of the substrate (22), producing a photosensitive resin mask (44) on the lightguide, having an opening (46) facing the location of the cavity to be produced, eliminating the zone of the lightguide which is not masked, eliminating the resin mask (44) and depositing on the second wall a reflecting material layer (38) using a precursor ion beam (48) of said material, inclined with respect to the surface of the guide.
11. Process according to claim 10, characterized in that the substrate (22) is of silicon or silica and in that the lightguide has a lower con-finement layer (24) of pure or optionally doped silica, a guide layer (26, 26a) of doped silica, alumina, silicon nitride or silicon oxynitride and an upper confinement layer (28) of pure or optionally doped silica, the guide layer (26, 26a) being inter-posed between the confinement layers and having s refractive index higher than that of the lower and upper layers.
12. Process according to claim 11, characterized in that etching is carried out with a fluorine-containing gas.
13. Process according to claim 10, characterized in that the guide is formed by a) depositing a lower confinement layer (24) on a substrate (22), b) depositing a guide layer (26) on the lower confinement layer, c) etching the guide B 11055.3 LC
layer (26a) so as to only retain the material of the guide layer upstream of the first wall (32) of the cavity (30) to be formed and d) depositing an upper confinement layer (28) on the structure obtained in c).
layer (26a) so as to only retain the material of the guide layer upstream of the first wall (32) of the cavity (30) to be formed and d) depositing an upper confinement layer (28) on the structure obtained in c).
14. Semiconductor laser diode stabilized by an external cavity (30) formed in a lightguide (20) for the propagation of a light beam (36) emitted by the diode in a given direction, said cavity having in the direction of the propagation a first (60) and a second 34) walls oriented perpendicular to said direction and, in section, approximately having the shape of a circular arc, the distance (L) separating the two walls being equal to the radius of curvature (R) of the second wall at the optical axis (37) of the external cavity (30), and a layer of a reflecting material (38) deposited solely on the second wall in order to reflect said light beam to the first wall, the second wall forming a concave reflecting surface, the first wall of the cavity constituting an input face (60) of the diode.
B 11055.3 LC
B 11055.3 LC
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR9115591A FR2685096B1 (en) | 1991-12-16 | 1991-12-16 | INTEGRATED OPTICAL MIRROR AND ITS MANUFACTURING METHOD. |
| FR9115591 | 1991-12-16 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2084816A1 true CA2084816A1 (en) | 1993-06-17 |
Family
ID=9420089
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002084816A Abandoned CA2084816A1 (en) | 1991-12-16 | 1992-12-08 | Integrated optical mirror and its production process |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US5323407A (en) |
| EP (1) | EP0547955A1 (en) |
| JP (1) | JPH06118211A (en) |
| CA (1) | CA2084816A1 (en) |
| FR (1) | FR2685096B1 (en) |
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| JP2002280649A (en) * | 2001-03-15 | 2002-09-27 | Nippon Telegr & Teleph Corp <Ntt> | Reflector of light and optical amplifier |
| GB2404035A (en) * | 2003-07-17 | 2005-01-19 | Dow Corning Ltd | Electro-optic gap-cell for waveguide deployment |
| US20050121424A1 (en) * | 2003-12-05 | 2005-06-09 | Scott Caldwell | Optical horned lightpipe or lightguide |
| US20060140569A1 (en) * | 2004-12-28 | 2006-06-29 | Intel Corporation | Planar waveguides with air thin films used as anti-reflective layers, beam splitters and mirrors |
| EP2881773B1 (en) * | 2013-12-03 | 2018-07-11 | ams AG | Semiconductor device with integrated mirror and method of producing a semiconductor device with integrated mirror |
| US20180031763A1 (en) * | 2016-03-15 | 2018-02-01 | Sutherland Cook Ellwood, JR. | Multi-tiered photonic structures |
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|---|---|---|---|---|
| US4485474A (en) * | 1981-12-10 | 1984-11-27 | General Dynamics/Electronics | Injection laser modulator with external resonator |
| JPS60246688A (en) * | 1984-05-22 | 1985-12-06 | Matsushita Electric Ind Co Ltd | Optical feedback type semiconductor laser device |
| JPS61132908A (en) * | 1984-12-03 | 1986-06-20 | Nippon Telegr & Teleph Corp <Ntt> | Antireflection film at end face of optical waveguide |
| US4726030A (en) * | 1986-07-21 | 1988-02-16 | Gte Laboratories Incorporated | External-coupled-cavity diode laser |
| FR2613826B1 (en) * | 1987-04-07 | 1990-10-26 | Commissariat Energie Atomique | MOTION SENSOR IN INTEGRATED OPTICS |
-
1991
- 1991-12-16 FR FR9115591A patent/FR2685096B1/en not_active Expired - Fee Related
-
1992
- 1992-12-08 CA CA002084816A patent/CA2084816A1/en not_active Abandoned
- 1992-12-10 US US07/988,460 patent/US5323407A/en not_active Expired - Fee Related
- 1992-12-11 JP JP4352309A patent/JPH06118211A/en active Pending
- 1992-12-14 EP EP92403393A patent/EP0547955A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| JPH06118211A (en) | 1994-04-28 |
| FR2685096B1 (en) | 1994-02-04 |
| EP0547955A1 (en) | 1993-06-23 |
| US5323407A (en) | 1994-06-21 |
| FR2685096A1 (en) | 1993-06-18 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 19960609 |